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Oligodendrocyte generation in the adult CNS provides a means to adapt the properties of circuits to changes in life experience. However, little is known about the dynamics of oligodendrocytes and the extent of myelin remodeling in the mature brain. Using longitudinal in vivo two-photon imaging of oligodendrocytes and their progenitors in the mouse cerebral cortex, we show that myelination is an inefficient and extended process, with half of the final complement of oligodendrocytes generated after 4 months of age. Oligodendrocytes that successfully integrated formed new sheaths on unmyelinated and sparsely myelinated axons, and they were extremely stable, gradually changing the pattern of myelination. Sensory enrichment robustly increased oligodendrocyte integration, but did not change the length of existing sheaths. This experience-dependent enhancement of myelination in the mature cortex may accelerate information transfer in these circuits and strengthen the ability of axons to sustain activity by providing additional metabolic support.

Glycogen storage disease type IV (GSD IV) is an autosomal recessive disorder caused by pathogenic variants in GBE1, resulting in deficient glycogen branching enzyme (GBE) activity and formation of abnormal glycogen (“polyglucosan”). GSD IV manifests across a spectrum of clinical dimensions—including hepatic, neurologic, muscular, and cardiac involvement—which vary in severity. The early‐onset forms, historically referred to as Andersen disease, present at different stages ranging from in utero to adolescence. The adult‐onset form, referred to as adult polyglucosan body disease (APBD), typically presents in middle to late adulthood. To date, no epidemiological study of GSD IV has been performed. Understanding the global prevalence of GSD IV is critical to increase disease awareness, improve diagnostic rates, inform therapeutic development, and engage pharmaceutical companies. In collaboration with the Rare Genomes Project at the Broad Institute of MIT and Harvard and the APBD Research Foundation, this study curated variants in GBE1 and calculated prevalence across nine genetic ancestry groups. The estimated global carrier frequency of GSD IV is 1 in 243 individuals, and the global genetic prevalence is 1 in 235 784 individuals. Based on the 2024 world population, the estimated number of affected individuals with GSD IV is approximately 34 800. These estimates highlight a significant underdiagnosis of GSD IV and underscore the urgent need for increased awareness of this metabolic disorder. This model of collaboration between researchers, patient advocacy organizations, and genetic data sharing programs provides a framework for estimating the prevalence of other rare diseases in the global population. Summary The estimated global carrier frequency of glycogen storage disease type IV is 1 in 243 individuals. The estimated global genetic prevalence of glycogen storage disease type IV is 1 in 235 784 individuals. Based on the 2024 world population estimates, there are approximately 34 800 individuals with glycogen storage disease type IV (including the adult‐onset form adult polyglucosan body disease). Genetic prevalence study of glycogen storage disease type IV. In collaboration with the Rare Genomes Project at the Broad Institute of MIT and Harvard and the APBD Research Foundation, this study queried and curated variants in GBE1 from ClinVar, HGMD, and gnomAD to calculate the genetic prevalence of glycogen storage disease type IV (GSD IV). The estimated global carrier frequency of GSD IV is 1 in 243 individuals, and the global genetic prevalence is 1 in 235 784 individuals. Based on the 2024 world population, the estimated number of affected individuals with GSD IV is approximately 34 800. These estimates include all forms of glycogen storage disease type IV, including the adult‐onset form adult polyglucosan body disease (APBD). Created in BioRender. Koch, R. (2025) https://BioRender.com/j0sg30n.

Destruction of oligodendrocytes and myelin sheaths in cortical gray matter profoundly alters neural activity and is associated with cognitive disability in multiple sclerosis (MS). Myelin can be restored by regenerating oligodendrocytes from resident progenitors; however, it is not known whether regeneration restores the complex myelination patterns in cortical circuits. Here, we performed time lapse in vivo two photon imaging in somatosensory cortex of adult mice to define the kinetics and specificity of myelin regeneration after acute oligodendrocyte ablation. These longitudinal studies revealed that the pattern of myelination in cortex changed dramatically after regeneration, as new oligodendrocytes were formed in different locations and new sheaths were often established along axon segments previously lacking myelin. Despite the dramatic increase in axonal territory available, oligodendrogenesis was persistently impaired in deeper cortical layers that experienced higher gliosis. Repeated reorganization of myelin patterns in MS may alter circuit function and contribute to cognitive decline.

In vertebrates, a family of related proteins called connexins form gap junctions (GJs), which are intercellular channels. In the central nervous system (CNS), GJs couple oligodendrocytes and astrocytes (O/A junctions) and adjacent astrocytes (A/A junctions), but not adjacent oligodendrocytes, forming a “glial syncytium.” Oligodendrocytes and astrocytes each express different connexins. Mutations of these connexin genes demonstrate that the proper functioning of myelin and oligodendrocytes requires the expression of these connexins. The physiological function of O/A and A/A junctions, however, remains to be illuminated.

The idea that myelination is driven by both intrinsic and extrinsic cues has gained much traction in recent years. Studies have demonstrated that myelination occurs in an intrinsic manner during early development and continues through adulthood in an activity-dependent manner called adaptive myelination. Motor learning, the gradual acquisition of a specific novel motor skill, promotes adaptive myelination in both the healthy and demyelinated central nervous system (CNS). On the other hand, exercise, a physical activity that involves planned, structured and repetitive bodily movements that expend energy and benefits one's fitness, promotes remyelination in pathology, but it is less clear whether it promotes adaptive myelination in healthy subjects. Studies on these topics have also investigated whether the timing of motor learning or physical exercise is important for successful addition of myelin. Here we review our current understanding of the relationship of motor skill learning and physical exercise on myelination.

To develop reparative therapies for multiple sclerosis (MS), we need to better understand the physiology of loss and replacement of oligodendrocytes, the cells that make myelin and the target of damage in MS. In vivo two-photon fluorescence microscopy allows direct visualization of oligodendrocytes in transgenic mouse models, and promises a deeper understanding of the longitudinal dynamics of replacing oligodendrocytes after damage. However, the task of tracking oligodendrocytes requires extensive human effort and is especially challenging in three-dimensional images. While several models exist for automatically annotating cells in two-dimensional images, few models exist to annotate cells in three-dimensional images and even fewer are designed for tracking cells in longitudinal imaging. Furthermore, the complexity of processes and myelin formed by individual oligodendrocytes can result in the failure of algorithms that are specifically designed for tracking cell bodies alone. Here, we propose a novel beta-mixture unsupervised oligodendrocyte segmentation system (BOSS) that can segment and track oligodendrocytes in three-dimensional images over time that requires minimal human input. We evaluated the performance of the BOSS model on a set of eight images obtained longitudinally. We showed that the BOSS model can segment and track oligodendrocytes similarly to a blinded human observer. Our method offers many advantages, as it does not require fully curated data, reduces computational time, and most importantly recapitulates cell dynamic patterns observed by manually tracking oligodendrocytes. Although BOSS was developed to apply to our studies on oligodendrocytes, we anticipate that it can be modified to study four-dimensional in vivo data of any brain cell.Competing Interest StatementThe authors have declared no competing interest.Footnotes* Figures are updated. Software is now available at GitHub.

The role of genetic testing in neurologic clinical practice has increased dramatically in recent years, driven by research on genetic causes of neurologic disease and increased availability of genetic sequencing technology. Genetic testing is now indicated for adults with a wide range of common neurologic conditions. The potential clinical impacts of a genetic diagnosis are also rapidly expanding, with a growing list of gene-specific treatments and clinical trials, in addition to important implications for prognosis, surveillance, family planning, and diagnostic closure. The goals of this review are to provide practical guidance for clinicians about the role of genetics in their practice and to provide the neuroscience research community with a broad survey of current progress in this field. We aim to answer three questions for the neurologist in practice: Which of my patients need genetic testing? What testing should I order? And how will genetic testing help my patient? We focus on common neurologic disorders and presentations to the neurology clinic. For each condition, we review the most current guidelines and evidence regarding indications for genetic testing, expected diagnostic yield, and recommended testing approach. We also focus on clinical impacts of genetic diagnoses, highlighting a number of gene-specific therapies recently approved for clinical use, and a rapidly expanding landscape of gene-specific clinical trials, many using novel nucleotide-based therapeutic modalities like antisense oligonucleotides and gene transfer. We anticipate that more widespread use of genetic testing will help advance therapeutic development and improve the care, and outcomes, of patients with neurologic conditions.

In the CNS, gap junctions couple oligodendrocytes and astrocytes (O/A) and adjacent astrocytes (A/A), but not adjacent oligodendrocytes, forming a so-called 'glial syncytium'. A gap junction is an intercellular channel composed of connexins; the composition of these channels depends on the particular connexins expressed by the apposing cells. Genetic experiments of nature and man have shown that the connexins expressed by both oligodendrocytes and astrocytes are required for the proper functioning of myelin and oligodendrocytes, but the underlying physiology of the channels formed by these connexins is unknown. In my thesis work, I have examined the role of connexin47 (Cx47) in the context of the glial syncytium by studying its expression, trafficking, and functional interactions in an in vitro cell model system. First, I have shown that the mutations in GJA12/Cx47 that cause Pelizaeus-Merzbacher-like Disease (PMLD), a devastating leukodystrophy, result in loss-of-function. In order to understand the context of this loss-of-function, I have defined the gap junction channels that most likely form at O/A (Cx47/Cx43 and Cx32/Cx30) and A/A (Cx43/Cx43 and Cx30/Cx30) junctions. Based on these results, I provide evidence that the underlying basis of PMLD is likely to be the loss of Cx47/Cx43 channels at O/A junctions. In addition, Cx32/Cx30 and Cx47/Cx43 channels have distinct functional properties, suggesting that these two channels may have different functions in vivo. Together, this work provides the framework to directly confirm the presence of these channels in vivo and define their functional role in the glial syncytium.